Planetary hours (Astrology)

The planetary hours are an ancient system in which one of the seven classical planets is given rulership over each day and various parts of the day. Developed in Hellenistic astrology, it has possible roots in older Babylonian astrology, and it is the origin of the names of the days of the week as used in English and numerous other languages. The classical planets are Saturn, Jupiter, Mars, the Sun, Venus, Mercury and the Moon, and they take rulership over the hours in this sequence. The sequence is from slowest- to fastest-moving as the planets appear in the night sky, and so is from furthest to nearest in the planetary spheres model. This order has come to be known as the "Chaldean order". As each day is divided into 24 hours and 24 ÷ 7 has a remainder of 3, the first hour of a day is ruled by the planet three places down in the Chaldean order from the planet ruling the first hour of the preceding day; i.e. a day with its first hour ruled by the Sun ("Sunday") is followed by a day with its first hour ruled by the Moon ("Monday"), followed by Mars ("Tuesday"), Mercury ("Wednesday"), Jupiter ("Thursday"), Venus ("Friday") and Saturn ("Saturday"), again followed by Sunday, yielding the familiar naming of the days of the week.